This invention relates to a ferromagnetic-material detector and more particularly to such a detector including a Hall-element and a bias magnet.
When a ferromagnetic article passes by such a detector, the output voltage changes due to the distortion of the magnet bias field. However, with no ferromagnetic article nearby, the Hall element output voltage is a large steady value. Output signal voltages are always superimposed on this large DC voltage. It is therefore customary to capacitor couple or otherwise AC couple the output of such detectors to an amplifier and/or another signal responsive device.
Besides the extra expense of providing such an AC coupling, the system can only respond to moving ferromagnetic articles that must travel at least fast enough that the AC coupling means can follow it without substantial attenuation.
It is therefore an object of the present invention to provide a ferromagnetic-material detector that is capable of using a large magnetic bias field and has no substantial DC output component.
It is also an object of this invention to provide a ferromagnetic-material detector having a magnet bias and a bucking current bias to provide lower values of DC output voltage upon which the signal voltage will be superimposed.